Beaming is not such a bad thing if you can get your drivers on-axis. And in many cases not such a bad thing if you want to go a little off axis, if you have ton of reflective surfaces around. As A$$hole stated knowing how to use it is another story, but not impossible. Not sure about the 50hz and 500hz range as there is many drivers that do it great.
There are some killer 2 way systems out there! Would I run a 6.5" mid/bass driver that low is another story.
Beaming is a simple consequence of unwanted interference of all the tiny point sources distributed over the cone surface. Directly on-axis, all points are approximately equal distant to the ear. But off-axis, the points are at different distances to the ear ... therefore, they can destructively interfere at high frequencies, reducing the off-axis response or narrowing the dispersion pattern.
Also remember beaming is a factor of cone diameter, not what the manufacture says the driver size is. Most 6.5-7 inch drivers will have about 4.5-5.5 inches of cone area, depends on their design. Things such as cone profile and material does have an effect on the off-axis response/beaming, but very little. Everything else in the design, well really doesn't matter. Feel free to ignore all marketing hype to the contrary. Bottom line with every postive/gain there is usually a negative/lost,
no way around Physics.
If you are convinced that your driver starts to "beam" at a frequency that's too low, and this effect is causing a problem in your installation, there's only one thing you can do: buy a driver with a smaller cone diameter.
Even if you are listening mostly on-axis, you might still care that beaming occurs at too low a frequency, because the power response (integrated off-axis response) is changing ... meaning that the reflections from the driver are changing as the driver starts to beam. Remember that in a reflective environment (like a car, with big glass reflectors all around your head), even if you think you're listening "on-axis", your ears are also receiving lots of reflected energy, know how/dealing with this is the key. You will either deal with it, change drivers or rebuild you interior (this is I'm doing:blush
Ok equation to calculate beaming:
An 6.5" driver with cone radiating area of 5.3 inches (Sd):
Speed of sound = approx 1145 feet per minute at sea level.
1145 *12 = 13740 (the speed of sound in inches)
Divide 13740 by the cone diameter (sd); so 13740/5.3= 2592.45 so beaming would start approximately around 2.6khz
As stated above the lower the driver plays and the more range you want it to reproduce the more adverse effects playing it to low will have on the upper range of the driver. Its all about you level of acceptance of these adverse effects.
I will use one of my own driver as an example. The new XR6.5M is a 6.5" Ultra wide-band driver. Cone area is right around 5.3" same as the above example. This beast will play from 50hz - up with easy, but do I like the sound of it that low. For a reference system no, everyday listening yes i could live with it very easily, but i would never run it that low at a reference volume level, as it playing it that low starts to have adverse effect on the midrange, causing it to sound a little rough on the edges, the higher frequencies starts to fall off a bit and sound a little un-natural to my ears.
Now raise the crossover point to 63hz and wow what a difference that little boost of the high-pass makes. Everything start to fall in place, open up, kick-drums tighten up, highs are crisp, midrange becomes natural and accurate and detailed greatly improves. Now boost that to round 70hz and it improves in a few areas, not as much as from 50hz to 63hz, but it still improves 70-80hz seem to be the sweet spot. My point once again is;
with every postive/gain there is usually a negative/lost, no way around Physics.. Play a driver to low with a wide range and you kill your upper range resolution. Like everything else it is all about finding that sweet spot.
Some drivers play wide ranges better then others and this is most do to motor design and cone material (believe it or not).
or i could just be talking crazy!
